Coronal Loops and The Coronal Heating Problem
A closed fieldline does not constitute a coronal loop; however, closed flux must be filled with plasma before it can be called a coronal loop. With this in mind, it becomes clear that coronal loops are a rarity on the solar surface, as the majority of closed-flux structures are empty. This means the mechanism that heats the corona and injects chromospheric plasma into the closed magnetic flux is highly localised. The mechanism behind plasma filling, dynamic flows and coronal heating remains a mystery. The mechanism(s) must be stable enough to continue to feed the corona with chromospheric plasma and powerful enough to accelerate and therefore heat the plasma from 6000 K to well over 1 MK over the short distance from the chromosphere and transition region to the corona. This is the very reason coronal loops are targeted for intense study. They are anchored to the photosphere, are fed by chromospheric plasma, protrude into the transition region and exist at coronal temperatures after undergoing intensive heating.
The idea that the coronal heating problem is solely down to some coronal heating mechanism is misleading. Firstly, the plasma filling over-dense loops is drained directly from the chromosphere. There is no coronal mechanism known that can compress coronal plasma and feed it into coronal loops at coronal altitudes. Secondly, observations of coronal upflows point to a chromospheric source of plasma. The plasma is therefore chromospheric in origin; there must be consideration of this when looking into coronal heating mechanisms. This is a chromospheric energization and coronal heating phenomenon possibly linked through a common mechanism.
| Why is the Sun's Corona so much hotter than the Sun's surface? |
Read more about this topic: Coronal Loop, Physical Features
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